How much is the newly introduced city tax?
Best to ask your hotel... the price differs, according to star-rating of the accommodation.
Yes that's true. We had a similar question on the Sorrento forum and I think it's about 3 euros each for a 4 star hotel per night for a maximum of 7 nights making it 21 euros each. I know the Covo dei Saraceni in Positano charges 5 euros each per night because I saw it on the booking page or the website and that's the place to look. Or, as already mentioned, you can contact the hotel.